Elektor_Mag_-_January-February_2021

lektor January & February 2021 55

of light that falls on it. The amount of

light varies periodically thanks to the

astable multivibrator. It will now also

be clear why we use incandescent

bulbs and not LEDs: an incandescent

bulb has a certain inertia that makes

the resistance change (and therefore

the change of the signal from left to

right and back) more smooth.

The construction of our pseudo-Leslie

is not critical. Only the lamps must be

mounted in such as way so that they

are close to their corresponding LDRs.

Here the use of a light-tight tube

ensures that ambient light cannot

throw a spanner in the works.

200557-04

On the left is a discretely-con-
structed astable multivibrator,
the frequency of which can be
set with P1 to between approx-
imately 1 Hz and 8 Hz. Note: P1
is a linear stereo potentiometer;
its wiring is shown in the centre
of Figure 8. The two light bulbs
serve primarily to vary the resis-
tance of the LDRs R3 and R4 and
also act as collector resistors for
the two transistors.

We come to the diagram on the
right of Figure 8. A mono signal
(not a stereo signal!) comes in
at C3 and is split by P2 (which
immediately acts as a kind
of balance control) into two
branches that go to the L and R
inputs of a stereo amplifier. Due to
the light-sensitive resistors, part of
the mono signal for each channel
is dissipated to ground; how much
depends of course on the resis-
tance value of the LDR and this,
in turn, depends on the amount

related products

> Book: Electronic Circuits for All

http://www.elektor.com/electronic-circuits-for-all

[1] Video of Tranquili-T in action: https://vimeo.com/272785420

[2] Donald Leslie, Wikipedia: https://en.wikipedia.org/wiki/Donald_Leslie

WEB LINKS

Questions or Comments?

Do you have questions or

comments regarding this

article? Then email Elektor at

[email protected].

Figure 8: The circuit (left) is relatively simple. The wiring for the potentiometer is shown in the centre. The connection to a stereo amplifier is shown on the
right.

Figure 7: The Leslie-box is a horizontally mounted

loudspeaker with a rotating cylinder that contains a sound

hole.